1. Field
The present invention relates to an information processing apparatus capable of charging a battery provided therein.
2. Description of the Related Art
A mobile information processing apparatus such as a mobile communication apparatus which is operated by electric power stored in a rechargeable battery is known. As such a rechargeable battery, a lithium-ion secondary battery is widely used. Such an apparatus notifies the amount of electric power stored in a lithium-ion secondary battery, and controls a charging operation. Specifically, in the case where a battery charger which converts electric power supplied from a commercial power source to charging electric power is connected to the apparatus, when the battery reaches full charge, the apparatus stops the charging operation to prevent the battery from being overcharged. Here, full charge means a state where the charging operation is completed. The battery charger supplies stable electric power which can charge the battery to the full charge state. During the charging operation, a charge indicator LED is turned ON.
On the other hand, when informed that the amount of stored electric power is small, the user of the apparatus connects the battery charger to the apparatus to perform the charging operation. After the apparatus was connected to the battery charger, the apparatus starts the charging operation and turns ON the charge indicator LED. When informed by turning-OFF of the LED of the completion of the charging operation, the battery charger is disconnected from the apparatus by the user. Also in the case of a charging operation by electric power stored in a dry cell, or by electric power generated by a hand crank generator, the charging operation is performed by electric power of a level similar to the charging electric power supplied from a commercial power source. Therefore, the charge control on the apparatus is performed in the same manner as the case of a commercial power source.
In the case where a rechargeable battery of a mobile information processing apparatus is charged by electric power generated by a solar cell which directly converts light energy to electric power by using the photoelectromotive force effect, the electric power is largely varied depending on light impinging on the solar cell, and hence it is known that the charge control is performed in a complex manner which is different from that in the case of charging by charging electric power converted from a commercial power source (for example, see JP-A-2008-228391). On the other hand, it is known that a solar cell and a rechargeable battery are directly connected to each other through a diode for preventing reverse flow of electric power (for example, see JP-A-8-088940).
In the method disclosed in the publication, JP-A-2008-228391, in the case where the electric power generated by the solar cell is small, however, the electric power may be insufficient for supplying electric power to be consumed in the complex charge control which is to be performed when the solar cell is connected, and the solar cell may consume electric power stored in the rechargeable battery.
The method disclosed in the publication, JP-A-8-088940, has a problem in that the charging operation is not performed at an appropriate charging voltage. When the charging operation is performed at an excessively high charging voltage, there is a possibility that the rechargeable battery is overcharged. When the charging operation is performed at an excessively low charging voltage, there is a possibility that the rechargeable battery is in a near full charge state for a long time period. When being overcharged or being in a near full charge state for a long time period, a lithium-ion secondary battery which is widely used in a mobile communication apparatus is deteriorated. Therefore, the charging operation by the method is not appropriate.
When such an apparatus is designed so that the voltage at which electric power is generated by a solar dell is slightly higher than that in the discharging process of a rechargeable battery, the above-discussed problem is mitigated. In the design, however, the storage battery cannot be charged to the full charge, and hence there arises a problem in that the storage capability of the battery cannot be sufficiently used.
In the method disclosed in the publication, JP-A-8-088940, moreover, charging and discharging operations are repeated without causing the storage battery to be charged to the full charge, with the result that there arises a problem in that the so-called memory effect possibly occurs in which the storage capability is reduced to the level of the amount of electrical power that is charged during the repeated charging and discharging operations. The memory effect is observed in a nickel-metal-hydride battery and a nickel-cadmium battery. In the above-described design in which the voltage at which electric power is generated by a solar dell is lowered, the problem is remarkable.